ARS | Publication request: Effect of microwave- and microwave-convection drying conditions on the total soluble phenolic content of 2-phase olive mill waste

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: February 10, 2011
Publication Date: June 14, 2011
Citation: Milczarek, R.R., Jackson, O.A., Mc Hugh, T.H. 2011. Effect of microwave- and microwave-convection drying conditions on the total soluble phenolic content of 2-phase olive mill waste. Annual Meeting of the Institute of Food Technologists.

Technical Abstract: The California olive oil industry produces tons of 2-phase olive mill waste (2POMW) every year as a byproduct of the olive oil milling process. 2POMW is rich in health-promoting phenolic compounds, but it is greater than 60% moisture (wet basis) in its native form and thus expensive to store and transport. Microwave- and combined microwave-convection drying have previously been explored as methods of preserving 2POMW. However, it heretofore was not known if such drying methods altered the nutritional profile of 2POMW. Thus, the objective of this study was to determine the effect of 3 different drying methods (microwave only, microwave-convection, and sequential microwave nly/microwave-convection) on the total soluble phenolic (TSP) content of 2POMW. Using a pilot-scale microwave dryer with a convection fan option, 3 replicate drying runs were performed for each of the 3 drying methods. In each run, 12 plates of 2POMW were arranged in randomly-selected locations within the microwave cavity. Drying temperature was 70°C for all runs. Plates were removed from the microwave at specific time intervals to track changes in TSP content over the course of drying. Both drying method and location in the microwave cavity were determined not to be significant (a = 0.05) sources of variation in TSP content. However, TSP content did change over time, with a significant decrease in TSP content (from 10.08 gallic acid equivalents/gram to 9.00 gallic acid equivalents/gram) from the beginning to the end of drying. There was an increase in TSP content in the 2POMW in the first 20 minutes of drying, though this increase was not statistically significant. These results indicated that all 3 methods of drying cause an 11% decrease in TSP content in 2POMW. This degradation of the nutritional content of 2POMW should be considered when processing this material.